Underwater Propulsion Apparatus Performance Enhancement Device and Associated Methods

ABSTRACT

A device that when fitted to a motor vessel&#39;s existing propulsion gear improves the performance and reduces potential damage and wear of underwater propeller shaft bearings, commonly referred to as “cutlass bearings” that are used on boats, ships, etc. Designed with radially mounted impeller blades around the periphery of the propeller shaft, the device creates a forced flow of water by centrifugal pumping action, which creates suction along the shaft abaft the cutlass bearing, thereby increasing the flow of water through the cutlass bearing. The device also greatly diminishes the probability that fouling around a propeller shaft will severely restrict water flow through the cutlass bearing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to patent application Ser. No.12/196,469, filed Aug. 22, 2008, now U.S. Pat. No. 7,837,524, whichitself claimed priority to provisional application Ser. No. 60/957,206,filed Aug. 22, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to devices and methods for marinepropulsion and liquid pumping, and, more particularly, to such devicesand methods for improving a performance of marine propulsion and pumpingsystems.

2. Description of Related Art

A cutlass bearing (common usage) is a special type of bearing usedextensively in marine and industrial applications for bearings operatingunder water or in other liquids. Cutlass bearings have no moving parts,and the bearing material is usually composed of a type of syntheticrubber and/or polymer, which supports the propeller shaft. Cutlassbearings are designed to utilize the lubricating properties of ahydraulic film of the surrounding water/fluid in which the bearing isoperating. For this reason channels are designed within the bearingsurface to promote the flow of liquids through the bearing, assuringproper lubrication while cooling the bearing and shaft surfaces at thesame time.

A common problem in propeller-driven vessels is fouling of the propellerand shaft with lines, rope, netting, plastic bags, etc. When propellershafts are fouled, often the fouling material is wound around the shaftin the section between the cutlass bearing and propeller hub. When thishappens, the flow of water through the cutlass bearing is restrictedand, in some cases, is cut off entirely. A vessel operator is sometimesmade aware of a fouling condition because of vibration in the propulsiongear and diminished performance. If he is aware of the fouling, theoperator will usually attempt to clear it by reversing the propulsiongear in an attempt to release the wound-up fouling, or, when that is notsuccessful, someone may go overboard to clear the fouled propulsiongear. Even a small amount of fouling right next to the cutlass bearingwill severely impede the flow of lubricating water because thecross-sectional area of the water channels in the bearing is relativelysmall. Small amounts of fouling around a propeller shaft, however, oftengoes unnoticed for extended periods. In this situation, the cutlassbearing suffers premature wear because of starvation of lubricatingwater. Furthermore, it is fairly common to have the aft ends of bearingsand bearing housings physically damaged and abraded when foulingmaterials are tightly wrapped around the propeller shaft for an extendedperiod.

Several devices have been designed and marketed for the purpose ofpreventing propeller and shaft fouling. They are generally based onrotary cutters that are attached to the shaft and act to cut the foulingmaterials as they begin to wrap around the shaft. Although some of thesedevices work well under the ideal conditions for which they weredesigned, they are not as effective in extreme conditions. These cuttingdevices generally require frequent repair and replacement in heavy useapplications such as those experienced by vessels operating in thecommercial sector. These devices also are not specifically designed toincrease the flow of water through the cutlass bearing.

Therefore, it would be beneficial to provide a simple, robust, anddependable device and method of manufacture and use for substantiallypreventing fouling of propellers, shafts, and cutlass bearings in marinevehicles.

SUMMARY OF THE INVENTION

The present invention is directed to a device that is mountable on apropeller shaft abaft (in back of) a cutlass bearing for improving aperformance of a propeller-driven propulsion apparatus. The devicecomprises an annular collar affixable for rotation with and dimensionedfor positioning about a shaft of a propeller in a longitudinal spacebetween a propeller hub and a cutlass bearing. A plurality of impellerblades are affixed to and extend radially out from the collar inspaced-apart relation. Each impeller blade has a length sufficient tonearly span the longitudinal space between the propeller hub and thecutlass bearing, leaving a gap between forward ends of the blades andthe cutlass bearing.

An annular ring is affixed in spanning relation to the forward ends ofthe impeller blades. A bridging element extends from one of the annularring and the cutlass bearing, and is positioned to longitudinally bridgethe gap between the blades forward ends and the cutlass bearing, therebysubstantially enclosing the gap.

In use, the impeller blades rotate in conjunction with the propellershaft, and in doing so they create a centrifugal flow of water outwardfrom the shaft, which in turn creates suction along the shaft surfaceand abaft the cutlass bearing. The suction draws water through the waterchannels in the bearing surface. The pumping action of the impellerblades, along with the greatly increased discharge area for water aroundthe periphery of the device, greatly decreases the likelihood thatfouling around the propeller shaft can restrict the flow through thecutlass bearing. Additionally, the outside edges of the impeller bladeshelp cut through and shear away the rotating fouling materials overtime, making it much more likely that the fouling material eventually becut and thrown off than it would when wound up on a relatively smoothshaft surface.

The device can be easily attached to the existing propulsion gear of avessel in order to improve the dependability and performance, and reducethe maintenance cost, of the propulsion gear. The invention can relateto that sector of vessels that utilize a propulsion system composed ofan inboard engine that turns a drive shaft exiting through the hull toturn a propeller. This type of propulsion apparatus normally uses one ormore cutlass bearings to support the shaft in its underwater section.

The device of the present invention increases water flow through normalcutlass bearings and decreases the likelihood that the water flow beseverely impeded by propeller and shaft fouling. The device, even withfouling around the propeller shaft, lessens the likelihood of bearingdamage owing to lack of water circulation. In order to achieve this, thedevice has multiple radially mounted blades that extend from the shaftsurface outward. These blades act as an impeller to create centrifugalpumping action in the water when the shaft is rotated. The periphery ofthe device also creates a large area for fluid discharge, which makesseverely flow restriction by fouling less likely.

The present device, when mounted abaft a cutlass bearing, shields thebearing from physical damage and erosion from fouling materials that maybecome wrapped around the propeller shaft. The blades of the devicemounted immediately abaft the bearing prevent fouling materials fromreaching the after end of the bearing and bearing housing, therebyprotecting the bearing and housing from direct abrasion.

The present device is robust and durable, and is able to remaineffective under extreme conditions and extended use. The device can beconstructed of, for example, stainless steel or othercorrosion-resistant metal alloys with welded or cast components and doesnot depend on sharp edges or close tolerances to remain effective.

The features that characterize the invention, both as to organizationand method of operation, together with further objects and advantagesthereof, will be better understood from the following description usedin conjunction with the accompanying drawing. It is to be expresslyunderstood that the drawing is for the purpose of illustration anddescription and is not intended as a definition of the limits of theinvention. These and other objects attained, and advantages offered, bythe present invention will become more fully apparent as the descriptionthat now follows is read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) is a cross-sectional side view a propulsion setup forinboard engine vessel.

FIG. 2 (prior art) cross-sectional end view of a propeller shaft,cutlass bearing, bearing housing, and water channel grooves.

FIG. 3 is a cross-sectional side view of a device of the presentinvention mounted on a propeller shaft.

FIG. 4 is an end view of the device of FIG. 3, illustrating a pluralityof impeller blades equally spaced around the periphery.

FIGS. 5A-5D depict various impeller blade embodiments: FIG. 5A, a flatplate blade of rectangular cross section with square outside edge; FIG.5B, a flat blade design with pointed ends; FIG. 5C, a flat blade designwith serrated edge; FIG. 5D, a curved blade.

FIGS. 6A,6B are end views of two impeller blade placement embodiments:

FIG. 6A, a blade placed with its radial axis collinear with a radialaxis of the shaft; FIG. 6B, an impeller blade with a radial axis at anangle with respect to the shaft radial axis.

FIGS. 7A,7B,7C illustrate three embodiments varying in longitudinalplacement of the impeller blades: FIG. 7A, the longitudinal axis of theimpeller blades parallel with the shaft longitudinal axis; FIG. 7B, thelongitudinal axis of the impeller blades at an angle with the shaftlongitudinal axis; FIG. 7C, the longitudinal axis of the impeller bladesis curved downward in a forward direction.

FIG. 8 illustrates another embodiment of the invention that includes afairing and a different impeller profile.

FIG. 9 illustrates an embodiment designed for intermediate shaftbearings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description of the preferred embodiments of the present invention willnow be presented with reference to FIGS. 1-9.

In FIGS. 1 and 2 are shown a typical marine vehicle arrangement of apropeller hub 101, drive shaft 102, cutlass bearings 103, bearinghousing 104, water inlet 105, and bearing-to-propeller dimension 106. S1and S2 are an aft strut and intermediate strut, respectively, whichsupport the bearing housings 104. Vessels with relatively short shaftsgenerally use only one bearing 51. Intermediate struts S2 and bearings103 are typically used on vessels with longer shafts. FIG. 2 furtherincludes an illustration of the water channel grooves 107 in the cutlassbearing 103.

FIG. 3 shows a cross-sectional side view of a propulsion setup with anembodiment of a device 10 of the present invention mounted in the space106 abaft the cutlass bearing 103 and before the propeller 100. For thistype of application the device 10 is manufactured to fit the availablespace 106, with sufficient clearance to provide for some lateral andlongitudinal movement of the shaft. A substantially annular collar 108is dimensioned for placement over the propeller shaft 102 and extendsapproximately half the distance of the total length of the distance 106.Multiple setscrews 109 in the collar 108 can be used to lock the deviceto the shaft 102. An annular back-plate 110 is welded to the collar 108and fits flush against the propeller hub 101 in this embodiment. As analternative affixing means of locking the device to the shaft 102, thedevice may be attached with multiple cap screws fastening the back-plate110 to tapped holes in the propeller hub 101.

Multiple equally spaced impeller blades 111 are disposed radially aroundthe device 10 and are welded to the collar 108 and back-plate 110. Alength 114 of the impeller blades 111 plus a width 115 of the backplate110 nearly spans the distance 106, leaving a gap 118 to allow forsufficient clearance between the impeller blades and bearing housing104. Forward ends 116 of the impeller blades 111 are welded to anannular ring 112, which holds the forward ends 116 of the impellerblades 111 in place. The annular ring 112 extends a short distance 119over an outside 117 of the bearing housing 104, thereby covering the gap118 between the impeller blades 111 and bearing housing 104.

FIG. 4 shows an end view of the device 10, with a plurality of impellerblades 111 substantially equally spaced around the shaft 102.

FIGS. 5A-5D depict various impeller blade cross-section embodiments thathave been contemplated for use in the invention, although these are notintended as limitations. A simple design 111 a (FIG. 5A) comprises aflat plate blade of rectangular cross section with square outside edge120 a. FIG. 5B illustrates a flat blade design 111 b with pointedoutside edges 120 b. FIG. 5C illustrates a flat blade design 111 c withserrated outside edges 120 c. FIG. 5D illustrates a curved blade 111 dwith a pointed outside edge 120 d.

FIGS. 6A,6B depict end views of two impeller blade placement embodiments10 a, 10 b, with the embodiment 10 a of FIG. 6A having a blade 111placed with a radial axis 121 collinear with a radius 122 extending fromthe shaft axis 123. In the embodiment 10 b of FIG. 6B, an impeller blade111′ is placed with its radial axis 121′ at an angle 126 with respect tothe radius 122 extending from the shaft axis 123. The angle 126 can bein a range of 0 to 45 degrees, for example.

FIGS. 7A-7C depict embodiments 10 c, 10 d in longitudinal placements ofthe impeller blades 111″, 111′″. The longitudinal axis 124″ of theimpeller blades 111″ can be parallel to the collar axis 127, which inuse is collinear with the shaft axis 123, as depicted in FIG. 7A, or thelongitudinal axis 124″ can be placed at an angle 125 with respect to thecollar axis 127, as depicted in FIG. 7B. Alternatively, the impellerblades 111″″ can be downwardly curved in a forward direction withrespect to the shaft axis 123, as depicted in FIG. 7C. The longitudinalblade angle 125 can range between 0 and 30 degrees, for example.

All the variations in blade cross section and placement depicted inFIGS. 5A-7C are capable of successfully achieving the objects of thisinvention. It is evident that the options in blade cross-section designand placement will only serve to enhance the performance of theinvention and provide more options for particular applications. Forexample, it would seem reasonable that blades and annular rings withsharp and/or serrated edges will cut through fouling better, whilecurved blade sections will be better at creating pumping action. It isalso evident that placing the blades at an angle to the longitudinalaxis of the shaft, or having helical blades, may be used to createpositive thrust with the device. The performance benefits of a certainblade design and placement scheme for a device can be weighed againstthe cost of its manufacture, durability, and maintenance.

Also contemplated in the design of the device are various shapedfairings that may be fixed to the existing bearing housing forward ofthe device. The benefits of such fairings include that they (1) providea better hydrodynamic profile, and lower resistance of the device, (2)improve the pumping ability of the invented device by serving as avolute of a pump, (3) help prevent fouling materials from jamming thedevice.

FIG. 8 shows another embodiment 10 e of the invention that includes afairing and alternative impeller profile. The annular fairing ring 113can be mounted to the bearing housing 104 with tapped screws. Forwardannular ring 112 e and impeller blades 111 e are designed to fit thesleeker profile, as compared with the embodiment 10 of FIG. 3, with theannular ring 112 e in this embodiment 10 e not extending over thebearing housing 104.

For intermediate bearings S2, where there is no propeller behind thebearing S2, the device 10 f can have a different profile. FIG. 9 depictsone embodiment 10 f of the invention designed for intermediate shaftbearings S2. A redesigned impeller profile 111 f and the absence of aback plate present a more hydrodynamic profile, while other elementssuch as 112 f, 113 f, and 109 remain similar to the embodiments shownabove. The collar 108 f can have a rounded rear edge 127 for improvedhydrodynamic performance.

It will be understood by one of skill in the art that the embodiment 10f of FIG. 9 could also be used in concert with any type of shaft-bornebearing, for example, in a pump, for enhancing the lubrication thereof.The structure for this type of device would be substantially the same asthat depicted in FIG. 9.

Design Theory

The cross-sectional area of the water flow channels in traditionalcutlass bearings is relatively small. For example, the height of thewater channels in cutlass bearings measured from the shaft surface isless than one-half inch for shafts up to 4 in. thick. Therefore, whenpropeller shafts become fouled with lines, ropes, or other materialbehind the cutlass bearing, the water flow through the bearing isquickly blocked. Without a steady flow of water, the bearing and shaftsurfaces are starved for lubrication, causing overheating and prematurewear in the bearing and shaft surfaces.

Conventional cutlass bearings depend only on the hydrodynamic force ofthe water flowing past them to provide water flow through the bearing.Many cutlass bearing housings have an inlet scoop designed on theforward end to promote positive water pressure on the forward side ofthe bearing. The amount of pressure developed at the forward end of thebearing is proportional to the speed of the water moving past thebearing. A slow-moving vessel, or one that is not moving, will thereforehave much less water flowing through the bearing that would a vesselmoving at high speed.

With the use of the instant invention several key improvements arerealized.

1. The aft end of the bearing is shielded from external fouling by theplacement of the impeller blades, which extend radially from the surfaceof the propeller shaft in the device. Restriction of water flow istherefore less likely and also direct wear damage to the bearing is lesslikely from fouling materials.

2. The use of the device prevents bearing damage from water starvationeven with fouling around the shaft and/or the device. This because theeffective discharge area for water coming through the bearing and out ofthe invented device is about 100 times greater than it is without thedevice.

3. The shaft-mounted impeller blades of the invented device causecentrifugal pumping action, which greatly increases the hydraulic forceacting on the water that is fed through the cutlass bearing. Thatcentrifugal force creates suction on the aft side of the bearing. Theamount of hydraulic pressure imparted by the centrifugal action of theimpeller blades is strictly dependent on shaft speed and not vesselspeed. Therefore, the benefits of the invention for slower-movingvessels is even more significant.

4. The sharp edges of rotating impeller blades make a much more hostileenvironment for fouling material that winds around the shaft than arethe relatively smooth surfaces of the shaft and bearing housings foundin traditional propulsion systems without the present device. Therefore,fouling is ripped apart by the rotating blades and does not remain inplace as long when the device of the present invention is mounted to thepropulsion gear.

Finally, another potential advantage of the device is that the design ofcutlass bearings can be improved because engineer-designers will have anew option of having forced water flow available instead of dependingonly on passive water flow as with conventional bearing designs.

In the foregoing description, certain terms have been used for brevity,clarity, and understanding, but no unnecessary limitations are to beimplied therefrom beyond the requirements of the prior art, because suchwords are used for description purposes herein and are intended to bebroadly construed. Moreover, the embodiments of the apparatusillustrated and described herein are by way of example, and the scope ofthe invention is not limited to the exact details of construction.

Having now described the invention, the construction, the operation anduse of preferred embodiments thereof, and the advantageous new anduseful results obtained thereby, the new and useful constructions, andreasonable mechanical equivalents thereof obvious to those skilled inthe art, are set forth in the appended claims.

1. A device for improving a performance of a propeller-driven propulsionapparatus comprising: an annular collar affixable for rotation with anddimensioned for positioning about a shaft of a propeller in alongitudinal space between a propeller hub and a cutlass bearing; aplurality of impeller blades extending radially out from the collar inspaced-apart relation, each impeller blade having a length sufficient tonearly span the longitudinal space between the propeller hub and thecutlass bearing, leaving a gap between forward ends of the blades andthe cutlass bearing, the blades comprising a spanning element positionedto substantially span the forward ends of the impeller blades; and abridging element extending from one of the spanning element and thecutlass bearing positioned to longitudinally substantially bridge thegap between the blades forward ends and the cutlass bearing, therebysubstantially enclosing the gap.
 2. The device recited in claim 1,wherein the collar has a longitudinal extent approximately one-half thelongitudinal space between the propeller hub and the cutlass bearing. 3.The device recited in claim 1, further comprising a plurality of setscrews insertable through radial apertures in the collar for affixingthe device to the propeller shaft.
 4. The device recited in claim 1,wherein the collar further comprises a substantially annular backportion positionable substantially flush against the propeller hub, theback portion having a radial extent approximately equal to a radialextent of the impeller blades.
 5. The device recited in claim 1, furthercomprising an annular backplate affixable to and positionablesubstantially flush against the propeller hub, the backplate having aradial extent approximately equal to a radial extent of the impellerblades.
 6. The device recited in claim 1, wherein the bridging elementcomprises a substantially annular protrusion extending forward from thespanning element to a forward end forward of a rear end of the cutlassbearing.
 7. The device recited in claim 1, wherein the bridging elementcomprises a substantially annular fairing ring positionable about thecutlass bearing and having a rear end rear of the blades forward ends.8. The device recited in claim 1, wherein each of the impeller bladeshas a shape selected from a group consisting of: a substantiallyrectilinear shape having a squared outside edge; a substantiallyrectilinear shape having a pointed outside edge; a substantiallyrectilinear shape having a serrated outside edge; and an arcuate shapecurving about a radial axis having a pointed outside edge.
 9. The devicerecited in claim 1, wherein the impeller blades have a longitudinal axisselected from one of substantially parallel with a longitudinal axis ofthe collar, at an acute angle with the collar longitudinal axis, andcurving downwardly forward relative to the collar longitudinal axis. 10.A method for improving a performance of a propeller-driven propulsionapparatus comprising: affixing a device about and for rotation with ashaft of a propeller, the device positioned at least partially in alongitudinal space between a propeller hub and a cutlass bearing, thedevice comprising a substantially annular collar and a plurality ofimpeller blades extending radially out from the collar in spaced-apartrelation, each impeller blade having a length sufficient to nearly spanthe longitudinal space between the propeller hub and the cutlassbearing, leaving a gap between forward ends of the blades and thecutlass bearing, the impeller blades comprising a spanning elementpositioned to substantially span the blades forward ends; andsubstantially enclosing the gap between the blades forward ends and thecutlass bearing.
 11. The method recited in claim 10, wherein the collarhas a longitudinal extent approximately one-half the longitudinal spacebetween the propeller hub and the cutlass bearing.
 12. The methodrecited in claim 11, further comprising affixing the device to thepropeller shaft using a plurality of set screws insertable throughradial apertures in the collar.
 13. The method recited in claim 10,wherein the device affixing comprises positioning a substantiallyannular back portion of the collar substantially flush against thepropeller hub, the back portion having a radial extent approximatelyequal to a radial extent of the impeller blades.
 14. The method recitedin claim 10, further comprising affixing an annular backplate to thepropeller hub in substantially flush relation, the backplate having aradial extent approximately equal to a radial extent of the impellerblades.
 15. The method recited in claim 10, wherein the bridging elementcomprises a substantially annular protrusion extending forward from thespanning element to a forward end forward of a rear end of the cutlassbearing.
 16. The method recited in claim 10, wherein the gap enclosingcomprises positioning a substantially annular fairing ring about thecutlass bearing, the fairing ring having a rear end rear of the bladesforward ends.
 17. The method recited in claim 10, wherein each of theimpeller blades has a shape selected from a group consisting of: asubstantially rectilinear shape having a squared outside edge; asubstantially rectilinear shape having a pointed outside edge; asubstantially rectilinear shape having a serrated outside edge; and anarcuate shape curving about a radial axis having a pointed outside edge.18. The method recited in claim 10, wherein the impeller blades have alongitudinal axis selected from one of substantially parallel with alongitudinal axis of the collar, at an acute angle with the collarlongitudinal axis, and curving downwardly forward relative to the collarlongitudinal axis.
 19. A device for improving a performance of a bearingthrough which liquid is intended to flow comprising: an annular collaraffixable for rotation with and dimensioned for positioning about ashaft behind a bearing; a plurality of impeller blades extendingradially out from the collar in spaced-apart relation, each impellerblade extending forward toward a rear end of the bearing, leaving a gapbetween forward ends of the blades and the bearing, the bladescomprising a spanning element positioned to substantially span theforward ends of the impeller blades; and a bridging element extendingfrom one of the spanning element and the bearing positioned tolongitudinally substantially bridge the gap between the blades forwardends and the bearing, thereby substantially enclosing the gap.
 20. Thedevice recited in claim 19, wherein a rear face of the collar is roundedtoward a rear end for decreasing hydrodynamic resistance.
 21. The devicerecited in claim 19, wherein the bridging element comprises an annularfairing ring positionable about the bearing and having a rear end rearof the blades forward ends.